Premium video content for our Spaceflight Now Plus subscribers.STS-1 anniversary eventThis 25th anniversary celebration of the first space shuttle launch took place April 12 at Space Center Houston. Speakers included Johnson Space Center Director Mike Coats, NASA Administrator Mike Griffin, Congressman Tom DeLay, Senator Kay Bailey Hutchison, STS-1 commander John Young and pilot Bob Crippen. Dial-up:Part 1 | Part 2Broadband:Part 1 | 2New lunar missionDuring this NASA news conference on April 10, agency officials unveil the Lunar Crater Observation and Sensing Satellite, or LCROSS, that will launch piggyback with the Lunar Reconnaissance Orbiter spacecraft in October 2008. LCROSS will use the launch vehicle's spent upper stage to crash into the moon's south pole in an explosive search for water.Dial-up | BroadbandLCROSS mission planDaniel Andrews, the LCROSS project manager from NASA's Ames Research Center, narrates this animation depicting the mission from launch through impact on the lunar surface.
Play videoSTS-1 crew looks backIn this highly entertaining program, commander John Young and pilot Bob Crippen of the first space shuttle crew tell stories and memories from STS-1. The two respected astronauts visited Kennedy Space Center on April 6 to mark the upcoming 25th anniversary of Columbia's maiden voyage.
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BY JUSTIN RAY
Follow the countdown and launch of the Lockheed Martin Atlas 5 rocket with the European ASTRA 1KR television broadcasting spacecraft. Reload this page for the latest on the mission.

THURSDAY, APRIL 20, 2006
A Lockheed Martin Atlas 5 rocket kept its appointment to launch a television broadcast satellite that will serve million of homes across Europe, successfully roaring off a Florida launch pad Thursday on the exact minute scheduled months in advance. Read our full story.

2219 GMT (6:19 p.m. EDT)
"Atlas team...you are the best in the world," says International Launch Services president Mark Albrecht. "This is 79 out of 79, an incredible record of achievment and success...Congratulations for another awesome performance."

2215 GMT (6:15 p.m. EDT)
T+plus 108 minutes, 14 seconds. SPACECRAFT SEPARATION! The European ASTRA 1KR television broadcast spacecraft has been deployed from the Centaur upper stage! This is the 79th consecutive successful launch for the Atlas rocket family dating back to 1993.

2215 GMT (6:15 p.m. EDT)
T+plus 108 minutes. Centaur has started a 0.6 deg per second spin up for payload release.

2206 GMT (6:06 p.m. EDT)
T+plus 99 minutes. Now five minutes from Centaur main engine start. This will be an 86-second firing of the RL10 engine.

2205 GMT (6:05 p.m. EDT)
T+plus 98 minutes. Centaur is beginning a turn to the orientation needed for the second engine firing.

2202 GMT (6:02 p.m. EDT)
T+plus 95 minutes. The reaction control system is increasing its duty cycle to settle propellant in Centaur for the upcoming burn.

2157 GMT (5:57 p.m. EDT)
T+plus 90 minutes. Centaur is reversing the direction of its thermal-conditioning roll motion as planned. The stage has performed a couple of these roll reversals during the coast; this is the final one.

2127 GMT (5:27 p.m. EDT)
T+plus 60 minutes. One hour since launch. The Centaur has flown over Africa. The upcoming second burn by the stage happens above the Central Indian Ocean. A map showing the ground track is available here.

2117 GMT (5:17 p.m. EDT)
T+plus 50 minutes. Centaur is in a gentle roll to keep the thermal heating even across the stage.

2045 GMT (4:45 p.m. EDT)
T+plus 18 minutes, 15 seconds. Centaur is reorienting itself following the first burn. And the stage is spinning up to one-and-a-half degree per second for thermal control during the coast.

2044 GMT (4:44 p.m. EDT)
T+plus 17 minutes, 54 seconds. MECO 1. Centaur's main engine has shut down following its first burn today. The rocket will coast in this preliminary orbit for nearly an hour-and-a-half before the RL10 is reignited to propel ASTRA 1KR into the targeted geosynchronous transfer orbit.

2043 GMT (4:43 p.m. EDT)
T+plus 16 minutes. Less than two minutes remain in this first burn of Centaur.

2027 GMT (4:27 p.m. EDT)
T+plus 20 seconds. The main engine is firing at full throttle and the solid rocket motor is burning well to generate a liftoff thrust of 1.2 million pounds.

2027 GMT (4:27 p.m. EDT)
LIFTOFF! Liftoff of Atlas 5 launching ASTRA 1KR -- a spacecraft to serve millions of homes across Europe as a television broadcaster in the sky. And the vehicle has cleared the tower!

2025 GMT (4:25 p.m. EDT)
T-minus 90 seconds. Launch control system is enabled. The Flight Termination System has been armed.

2025 GMT (4:25 p.m. EDT)
T-minus 1 minute, 50 seconds. The automatic computer sequencer is in control of all the critical events through liftoff.

2025 GMT (4:25 p.m. EDT)
T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching to internal power. Liquid oxygen and liquid hydrogen topping for Centaur will be stopped in about 10 seconds.

2024 GMT (4:24 p.m. EDT)
T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for flight. Also, the RP-1 tank is being pressurized to flight level.

2020 GMT (4:20 p.m. EDT)
Veteran launch conductor Ed Christiansen, seated in the Atlas Spaceflight Operations Center four miles from the pad, has polled the various console operators to ensure all systems are ready to proceed with the countdown. The 'go' status was passed to launch director Jerry Jamison located above and behind the launch team in the management room.

2018 GMT (4:18 p.m. EDT)
The ASTRA 1KR satellite is confirmed on internal power and ready to launch.

2013 GMT (4:13 p.m. EDT)
T-minus 4 minutes and holding. The countdown has entered the planned 10-minute hold to give the launch team a chance to review all systems before pressing ahead with liftoff.

2011 GMT (4:11 p.m. EDT)
All three cryogenic fuel tanks aboard the rocket are now reported at flight level.

2011 GMT (4:11 p.m. EDT)
The fuel-fill sequence for the first stage main engine is reported complete.

2007 GMT (4:07 p.m. EDT)
Twenty minutes to go.

2002 GMT (4:02 p.m. EDT)
The latest guidance and steering data have been loaded into the rocket's flight computer based on today's upper level wind conditions.

2001 GMT (4:01 p.m. EDT)
Flight control final preps are complete. And the fuel-fill sequence is starting for the Russian-designed RD-180 main engine.

1957 GMT (3:57 p.m. EDT)
The countdown is continuing very smoothly and on schedule today. Things are fairly quiet right now following the completion of fueling operations.

1947 GMT (3:47 p.m. EDT)
T-minus 30 minutes and counting. The countdown clocks are heading to the T-minus 4 minute mark where a planned 10-minute hold will occur. The weather is beautiful and there are no technical issues being reported by the launch team. Liftoff of Atlas 5 with the ASTRA 1KR spacecraft remains set for 4:27 p.m. EDT.

1937 GMT (3:37 p.m. EDT)
Fast-filling of the first stage liquid oxygen tank has been completed. Topping mode is now underway.

The countdown is being controlled from the Atlas Spaceflight Operations Center, or ASOC, located about four miles south of the Complex 41 pad. Members of the launch team have an average of 16-17 years of operations experience.

1916 GMT (3:16 p.m. EDT)
First stage liquid oxygen tank is now half full. Chilled to Minus-298 degrees F, the liquid oxygen will be used with RP-1 kerosene by the RD-180 main engine on the first stage during the initial four minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket during the countdown rehearsal earlier this month.

1914 GMT (3:14 p.m. EDT)
Chilldown of the liquid hydrogen system is now complete, allowing the super-cold fuel to begin filling the Centaur upper stage.

1859 GMT (2:59 p.m. EDT)
Ten percent of the first stage liquid oxygen tank has been filled so far. The stage's bronze skin is icing over as the supercold liquid oxygen flows into the vehicle.

1857 GMT (2:57 p.m. EDT)
Now 90 minutes to launch.

1855 GMT (2:55 p.m. EDT)
The Centaur liquid oxygen tank has now reached the 95 percent level. The topping off process is starting.

1850 GMT (2:50 p.m. EDT)
The chilldown conditioning of liquid hydrogen propellant lines at Complex 41 is now starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 13,000 gallons of the cryogenic propellant.

1847 GMT (2:47 p.m. EDT)
The chilldown conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin pumping super-cold liquid oxygen into the Atlas 5's first stage. The Atlas liquid oxygen tank is the largest tank to be filled today. It holds about 50,000 gallons of cryogenic oxidizer for the RD-180 main engine.

1829 GMT (2:29 p.m. EDT)
Following the thermal conditioning of the transfer pipes, filling of the Centaur upper stage with 4,300 gallons of liquid oxygen has begun at Cape Canaveral's Complex 41.

The liquid oxygen -- chilled to Minus-298 degrees F -- will be consumed during the launch by the Centaur's single RL10 engine along with liquid hydrogen to be pumped into the stage a little later in the countdown. The Centaur will perform two firings today to deliver the ASTRA 1KR spacecraft into geosynchronous transfer orbit.

1822 GMT (2:22 p.m. EDT)
The Centaur liquid oxygen pad storage area has been prepped. The next step is conditioning the transfer lines, which is now beginning to prepare the plumbing for flowing the cryogenic oxidizer.

1817 GMT (2:17 p.m. EDT)
Chilldown thermal conditioning of the mobile launch platform upon which the rocket stands is beginning. This is meant to ease the shock on equipment when supercold cryogenic propellants start flowing into the rocket a short time from now.

1817 GMT (2:17 p.m. EDT)
T-minus 120 minutes and counting! Countdown clocks are running again for launch of the Atlas 5 rocket and ASTRA 1KR television broadcast satellite to serve Europe. Clocks have one more built-in hold planned at T-minus 4 minutes. That pause will last 10 minutes, giving the launch team one last chance to catch up on work running late or deal with any problems.

1812 GMT (2:12 p.m. EDT)
All console operators in the Atlas Spaceflight Operations Center reported a "ready" status during the pre-fueling poll just completed by the launch conductor. Launch director Jerry Jamison gave his 'go' as well.

1810 GMT (2:10 p.m. EDT)
The Lockheed Martin launch conductor Ed Christiansen is briefing his Atlas launch team on countdown procedures before entering into the final two hours.

1802 GMT (2:02 p.m. EDT)
Now half way through this scheduled 30-minute hold. Launch team readiness polls are coming up shortly.

We've posted another gallery of pre-launch images. This one shows the Atlas 5 rocket on the pad this morning. See the pictures here.

1758 GMT (1:58 p.m. EDT)
There will be two Collision Avoidance, or COLA, periods during today's launch window. These are blocks of time in which liftoff cannot occur because the rocket's trajectory would take it too close another object already in space.

The COLAs are 5:09:46 to 5:16:10 p.m. EDT and 6:47:31 to 6:54:25 p.m. EDT.

1747 GMT (1:47 p.m. EDT)
T-minus 2 hours and holding. A planned 30-minute built-in hold for the countdown has just started. This scheduled pause is designed to provide some margin in the countdown timeline to deal with technical issues or recover from work running behind. The count will resume at 2:17 p.m. EDT.

Another hold is planned at the T-minus 4 minute point. Launch is still set for 4:27 p.m. EDT.

1742 GMT (1:42 p.m. EDT)
The final members of the launch pad crew are preparing to leave Complex 41 now.

1733 GMT (1:33 p.m. EDT)
Range Safety are performing the hold-fire checks. This ensures safety officers will have the capability of halting the countdown if a problem occurs.

1727 GMT (1:27 p.m. EDT)
The countdown is now inside three hours to launch.

We've posted a gallery of images taken during yesterday's rollout of the Atlas 5 rocket to the launch pad. See the pictures here.

1704 GMT (1:04 p.m. EDT)
A C-band test with the Range has been completed. This system allows the Air Force-controlled Eastern Range to track the Atlas 5 rocket during launch.

1652 GMT (12:52 p.m. EDT)
Roadblocks around the blast danger area of the launch pad are being established.

1627 GMT (12:27 p.m. EDT)
Launch of Atlas 5 is now four hours away. Internal battery checks are now underway. And technicians have just completed preps on the Centaur upper stage liquid oxygen and liquid hydrogen systems.

1608 GMT (12:08 p.m. EDT)
The launch team is beginning a test of the S-band telemetry relay system.

1600 GMT (12:00 p.m. EDT)
Good afternoon from the Kennedy Space Center press site, located about four miles northwest of the Atlas 5 rocket's Complex 41 launch pad. It is an absolutely beautiful spring day here in Central Florida. Skies are bright blue, temperatures are warm and there's a light breeze blowing. Weather is ideal for launch right now.

The countdown is continuing on schedule for liftoff in just under four-and-a-half hours.

1440 GMT (10:40 a.m. EDT)
The early phase of the countdown is progressing quietly at the Cape. We'll begin more frequent updates live from Kennedy Space Center in a little while.